Resolution of lysine



United States RESOLUTION OF LYSENE Melvin C. Baker, Niagara Falls, N.Y., assignor to E. I. du Pont de Nemours and Company, Wilmington, Bah, a corporation of Delaware No Drawing. Filed Sept. 16, 1957, Ser. No. 683,960

'7 Claims. (Cl. 260-534) This invention relates to the resolution of lysine employing an optically active glutamic acid as the resolving agent.

Emmick U.S. Patent 2,556,907 and Rogers US. Patent 2,657,230 disclose resolving lysine by reacting, for example, L-glutamic acid with a mixture of L-lysine and D-lysine, e.g., racemic lysine, and fractionally crystallizing the resulting mixture of lysine glutamates from aqueous methanol. The optically active lysine glutamates obtained can be used as such, e.g., as food flavoring agents, or they may be treated by known methods to recover their lysine and glutamic acid components. Usually, the recovered L-lysine is retained as prodnot and the recovered L-glutamic acid and D-lysine (after racemization) are recycled for use in further resolution operations.

The above patents show employing a maximum of 1 mole of glutamic acid per mole of lysine (considering both L- and D'lysine) and the Rogers patent states that even a slight excess of glutamic acid seriously retards crystallization, The present invention is based upon the discovery that the use of an excess of glutamic acid in the resolution mixture is distinctly beneficial if employed under proper conditions.

It is an object of the invention to provide an improved method of resolving lysine. A particular object is to provide an improved method of resolving lysine employing an optically active glutamic acid as resolving agent, particularly a method employing an excess of glutamic acid. Other objects will be apparent from the following description. The objects of the invention are accomplished by reacting a mixture of D- and L-lysines, e.g., a racemic mixture, with an excess of an optically active glutamic acid and fractionally crystallizing the resulting mixture of L- lysine and D-lysine salts of the glutamic acid from a methanol-water solvent mixture containing an amount of ammonia at least stoichiometrically equal to the excess glutamic acid present in the resolution mixture. If the resolution mixture also contains some pyroglutamic acid, as will generally be the case when the glutamic acid component of the L-lysine and D-lysine glutamates separated by the resolution is recovered and reused as resolving agent, the amount of ammonia present in the resolution mixture should be at least stoichiometrically equal to the sum of the excess glutamic acid and the pyroglutamic acid present. 7

The presence ofeven a slight excess of glutamic acid, i.e., more than 1 mole per mole of lysine (both the D- and the L-lysine), in the resolution mixture was previously known to retard crystallization seriously and it was, therefore, thought that any excess of glutamic acid should be avoided. The present invention is based upon the discovery that the presence of a substantial excess of glutamic acid is distinctly beneficial, provided there is also present an amount of ammonia at least equal stoichiometrically to the excess of glutamic acid plus any pyroglutamic acid present. It has been found that when excess glutamic 2,942,024 Patented June 21, 1960 ice 2 acid is present under these conditions, the optically active lysine glutamate product of the fractional, crystallization step is readily filtered, long crystallization times are not necessary and product of good optical purity is obtained in good yields. A further advantage is that the presence of relatively large amounts of pyroglutamic acid can be tolerated. Although pyroglutamic acid is not an effective resolving agent, its presence has a beneficial salting out effect resulting in somewhat higher recoveries of the desired optically active lysine glutamate.

The resolution method of the invention will generally involve employing from 1.1 to 3 moles of the optically active glutamic acid, i.e., a 10 to 200% excess, per mole of lysine (considering both D- and L-lysine). Still larger proportions of glutamic acid can be used but are not recommended for economic reasons. It is preferred to use from 1.2 to 2 moles of glutamic acid (a 20 to 100% excess) per mole of lysine.

The amount of ammonia used should be at least equal, on a stoichiometric or molar basis, to the sum of the excess of glutamic acid plus any pyroglutamic acid also present. Amounts up to 8 times the molar equivalent of the sum of the excess glutamic acid and the pyroglutamic acid are satisfactory. Even larger amounts are usable but are not recommended because they usually decrease product yield too greatly. The preferred amounts range from 1.2 to 5 moles of ammonia per mole of excess glutamic acid plus pyroglutamic acid. Thus, in a system having present 1.25 moles of glutamic acid and 0.25 mole pyropglutamic acid per mole of lysine, there would be a 0.25 mole excess glutamic acid. This excess plus the 0.25 mole pyroglutamic acid (total of 0.5 mole) would dictate the presence of from 0.6 to 2.5 moles of ammonia in order to meet the preferred conditions respecting the amount of ammonia to be used, i.e., 1.2 to 5 moles per mole of excess glutamic acid plus pyroglutamic acid.

The method of the invention is illustrated by the following examples.

EXAMPLE 1 An aqueous solution (143 g.) containing 73 g. (0.5 mole) of DL-lysine was mixed with 110 g. (0.75 mole) and L-glutamic acid in a flask equipped with a mechanical stirrer and a reflux condenser. The mixture was diluted with 46 g. water and 31 g. of 28% aqueous ammonia (0.5 mole NH was added. The mixture was stirred at 60 C. (constant temperature bath) until all glutamic acid had dissolved when 585 g. methanol was added and stirring was continued until the temperature again reached 60 C. The resulting solution was seeded with 1 g. L-lysine L-glutamate monohydrate seed crystals and stirred for 6 hours at 60 C. The precipitated L-lysine L-glutamate monohydrate was filtered (about 8 minutes required), washed once with 250 ml. of methanol (80 volumes of methanol and 20 volumes of water), reslurried once with 500 ml. 80% methanol and filtered; and then reslurried once with 250 ml. of methanol and finally filtered and dried. The product L-lysine L- glutamate monohydrate weighed 49 g. (63% yield, based on the L-lysine originally present) and had an optical purity of 95.9%.

The resolution system of the above example contained 22.2% solids by weight, and the aqueous methanol solvent contained 75.4% methanol by weight. There were present 0.25 mole excess glutamic acid, no pyroglutamic acid, and 0.5 mole ammonia. The yield and optical purity of the product were good, despite the presence of excess glutamic acid and the relatively short crystallization time (6 hours); and the product filtered readily from the resolution mixture. Had no ammonia been present most of the excess glutamic acid would not Table 1 EFFECTS OF VARYING THE AMOUNT OF GLUTAMIO ACID Yields are based upon the amount of L-lysine present in the resolution system.

' The results of Table I show that when ammonia is also present it is distinctly advantageous, yield-wise, to employ an excess of glutamic acid and that under these conditions good product which filters rapidly can be' obtained in the short crystallization time of 6 hours.

Other resolutions employing 80% methanol (by weight) as solvent in systems containing 20% solids were carried out following the general procedures of Example 1, including the 6 hours crystallization time at 60% C. In all of these resolutions, an excess of glutamic acid was employed with various amounts of ammonia and with or without pyroglutamic acid present. Results are reported in Table II in which Examples 1 and 4 are included for comparison purposes.

Table II EXAMPLES USING EXCESS GLUTAMIO ACID Moles/Mole of Lysine Percent Product Percent Optical Filter- Example Yield Purity ability,

Glut. Pyroglut. NH; min. Acid Acid 1. 5 0 1. 0 63 95. 9 ca. 1.25 0 1.0 76 94. 2 ca. 8 1.125 0.126 1. 25 62 93. 7 ca. 8 1.25 0.25 0.5 66 94.6 ca. 8

*Yields based on L-lysine present in the resolution system.

The above examples illustrate the use of L-glutamic acid. This is the preferred resolving agent since its use results in the preferential precipitation of the glutamic of L-lysine, the most generally desired salt. However, if the glutamate of D-lysine is desired, the process can be practiced in exactly the same manner using D-glutamic acid as the resolving agent. When this is done the D-lysine salt of D-glutamic acid is preferentially precipitated.

The advantages resulting from the use of excess glutamic acid in accordance with the invention are realized to a significant extent regardless of the temperature at which the fractional crystallization is carried out. In general, temperatures from about room temperature to the boiling point (at atmospheric or slightly higher pressures) of the solvent can be used. However, the benefits of employing excess glutamic acid under the conditions stated are greatest when the fractional crystallization is carried out at temperatures ranging from 45 to C., and such temperatures are preferred.

An aqueous methanol solvent should be employed. The proportions of methanol to water in the solvent can be varied considerably as disclosed in Patents 2,556,907 and 2,657,230. Generally, the solvent mixture will contain methanol and water in the proportions of 1 to 20,

preferably 2 to 10, volumes of methanol per volume of water.

As indicated previously, the resolution mixture may or may not contain pyroglutamic acid. Generally, when recycling the glutamic acid resolving agent, a significant amount of pyroglutamic acid will be present. The present method can be successfully practiced when relatively large amounts of pyroglutamic acid are present, e.g., up to 2 moles per mole of glutamic acid.

The invention provides an improved method for resolving lysine whereby a high-purity, readily filterable optically active lysine glutamate product can be obtained in good yield from the resolution mixture in a crystallization time substantially shorter than that required in prior methods. Whereas from 8 to 48 hours are required to complete crystallization in prior resolution methods employing glutamic acid, only 4 to 6 hours are required in the present method at the preferred temperatures.

Longer crystallization times can be used but are not necessary.

I claim:

1. In a method for resolving lysine in which a mixture acid, the improvement comprising employing from 1.1 to V 3 moles of said optically active glutamic acid per mole of lysine in the presence of from 0 to 2 moles of pyroglutamic acid per mole of said glutamic acid, and effecting the fractional crystallization in the presence of from 1 to 8 moles of ammonia for each mole of said glutamic acid which is in excess of 1 mole per mole of lysine and from 1 to 8 moles of ammonia for each mole 'of pyroglutamic acid. p

2. The method of claim 1 employing 12m 2 moles of glutamic acid per mole of lysine.

3. The method of claim 1 employing from 1.2 to 5 moles of ammonia for each mole of glutamic acid which is in excess of 1 mole per mole of lysine and from 1 to 8 moles of ammonia for each mole of pyroglutamic acid.

4. The method of claim 1 employing L-glutamic acid.

5. The method of claim 2 employing L-glutamic acid.

6. The method of claim 3 employing L glutamic acid.

7. The method of claim 6 wherein the fractional crystallization is carried out at a temperature of from 45 to 75 C. 1

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A METHOD FOR RESOLVING LYSINE IN WHICH A MIXTURE OF L- AND D-LYSINES IS REACTED WITH AN OPTICALLY ACTIVE GLUTAMIC ACID AND THE RESULTING L-LYSINE AND D-LYSINE SALTS OF SAID GLUTAMIC ACID ARE FRACTIONALLY CRYSTALLIZED FROM A METHANOL-WATER MIXTURE TO RECOVER L-LYSINE L-GLUTAMATE WHEN THE OPTICALLY ACTIVE GLUTAMIC ACID EMPLOYED IS LGLUTAMIC ACID, AND TO RECOVER D-LYSINE D-GLUTAMATE WHEN THE OPTICALLY ACTIVE GLUTAMIC ACID EMPLOYED IS D-GLUTAMIC ACID, THE IMPROVEMENT COMPRISING EMPLOYING FROM 1.1 TO 3 MOLES OF SAID OPTICALLY ACTIVE GLUTAMIC ACID PER MOLE OF LYSINE IN THE PRESENCE OF FROM 0 TO 2 MOLES OF PYROGLUTAMIC ACID PER MOLE OF SAID GLUTAMIC ACID, AND EFFECTING THE FRACTIONAL CRYSTALLIZATION IN THE PRESENCE OF FROM 1 TO 8 MOLES OF AMMONIA FOR EACH MOLE OF SAID GLUTAMIC ACID WHICH IS IN EXCESS OF 1 MOLE PER MOLE OF LYSINE AND FROM 1 TO 8 MOLES OF AMMONIA FOR EACH MOLE OF PYROGLUTAMIC ACID. 